(a) Field of the Invention
The present invention relates to an automatic transmission for vehicles that achieves eight forward speeds and four reverse speeds. More particularly, the present invention relates to an automatic transmission for vehicles, whose weight, length, and manufacturing cost are reduced as a consequence of simplifying a structure thereof by removing a torque converter.
(b) Description of the Related Art
A transmission of a vehicle is disposed between an engine and a drive shaft. The transmission converts engine torque into torque and speed suitable for a running state of the vehicle, and transmits the torque and speed to a driving wheel.
That is, the transmission achieves a neutral state so as to enable the engine to be started, forward speeds by suitably changing the driving torque of the engine so as to enable the vehicle to move forwardly, and reverse speeds by suitably changing the driving torque of the engine so as to enable the vehicle to move backwardly.
Transmissions for vehicles are divided largely into a manual transmission where a driver directly performs a shifting action, and an automatic transmission where a detecting means disposed at a preferable position in the vehicle detects the driving state of the vehicle and a transmission control unit (TCU) automatically performs the shifting action based on the driving state. The present invention relates to an automatic transmission.
Generally, an automatic transmission or vehicles includes a torque converter, a power train connected to the torque converter and achieving a plurality of gear ratios, and a hydraulic control system selectively operating operation members of the power train according to the driving state of the vehicle.
The automatic transmission also includes a compound planetary gear set formed by combining at least two simple planetary gear sets to achieve the required multiple speeds. The power train includes a plurality of frictional members, and the hydraulic control system selectively operates the frictional members of the power train according to the driving condition.
A variety of such power trains and hydraulic control systems have been developed by vehicle manufacturers according to their own schemes. □
Currently, four-speed and five-speed automatic transmissions are most often found on the market. However, six-speed automatic transmissions have also been realized for enhancement of performance of power transmission and for enhanced fuel mileage of a vehicle.
In spite of excellent merits, the automatic transmission has disadvantages in efficiency. Currently, automatic transmissions that have the excellent efficiency of a manual transmission as well as the convenience of an automatic transmission are under investigation through using a plurality of frictional members (i.e., clutches and brakes) and shift automation means mounted to a conventional manual transmission.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.